1. Field of the Invention
The present invention relates to a zirconia diaphragm structure, a method of producing the same, and a piezoelectric/electrostrictive film element including the zirconia diaphragm structure. In particular, the invention is concerned with such a diaphragm structure having a thin zirconia diaphragm that is free of buckling, cracks and other defects, and a method of producing the diaphragm structure, and is also concerned with a high-quality piezoelectric/electrostrictive film element including such a zirconia diaphragm structure.
2. Discussion of Related Art
A diaphragm structure having a substrate or base with at least one window or opening formed therethrough, and a thin diaphragm plate formed of a flexible material so as to close the window or windows, has been widely used for various kinds of sensors. In recent years, this diaphragm structure has been increasingly used for piezoelectric/electrostrictive actuators. When the diaphragm structure is used as a component of a sensor, the sensor has appropriate means for detecting the amount of bending or flexural displacement of a diaphragm of the diaphragm structure, which displacement is caused by an object (e.g., voltage) to be measured by the sensor. When the diaphragm structure is used as a component of a piezoelectric/electrostrictive actuator, the diaphragm of the diaphragm structure is deformed or deflected by a piezoelectric/electrostrictive element formed on the diaphragm. For example, the actuator utilizes a change in the pressure in a pressure chamber formed within the diaphragm structure.
The diaphragm structure as described above may be produced by forming an integral body consisting of the substrate serving as a base or support, and a film member which is supported by the substrate and which provides the diaphragm. For improved operating reliability, and increased heat resistance and corrosion resistance, the diaphragm structure is desirably formed as a fired integral ceramic body, as proposed in U.S. Pat. No. 4,894,635 (corresponding to JP-A-63-292032) owned by the assignee of the present application, and co-pending U.S. patent application No. 08/239,856 (corresponding to JP-A-5-29675) assigned to the present assignee. These documents disclose a piezoelectric/electrostrictive film element in the form of a fired integral body of a ceramic material, which is used for a pressure sensor and a piezoelectric/electrostrictive actuator.
The integral ceramic diaphragm structure as described above is generally formed by laminating a ceramic green substrate having a window with a thin ceramic green sheet for closing the window, to thus form an integral green laminar ceramic body having a diaphragm portion which closes the window at one of the opposite open ends of the window. The green laminar ceramic body is then fired into the integral diaphragm structure. The inventors of the present invention found that the thus prepared diaphragm structure tends to suffer from buckling or cracking at the diaphragm portion. The buckling and cracking at the diaphragm portion are detrimental to the intended function or operation of the diaphragm, resulting in reduced operating reliability.